smaller mp4 files(5 posts)
The short answer is: you can't. The mp4 compression scheme is a lossy compression scheme, just like jpeg and mp3. As you start reducing the bitrate, the compression scheme must make more sacrifices in quality. Lowering the resolution reduces the amount of data that needs to be compressed so that you get better quality at the same bitrate. There have to be trade-offs made between size, resolution, and quality.
What are you trying to do? I might be able to help.
teddy, there are many flavors of MPEG-4 video, which one are you using? Changing to a different format is not going to save you a lot of space. MPEG-4 video is state of the art and even competing codecs do not give better compression rates.
Some compression schemes can use advanced features to save space, but these features put an extra burden on the decompression hardware. For example, with MPEG-4 AVC you can use CABAC, but some decoders can't handle this. As far as I know, the iPod can't playback this kind of file.
Here's another idea. If you are using a constant bitrate (CBR), changing to a variable bitrate (VBR) should save space on most videos without a loss of quality. The trade-off here is again increased requirements on the decoding hardware, but decoders that can handle VBR are quite common.
Finally, if you have a target size that you need, e.g. 700 MB for a CD-ROM, then set your encoder to that size and let it choose the best quality it can.
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